diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/torture.txt | 147 |
1 files changed, 140 insertions, 7 deletions
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index a41a0384d20c..af712a3c5b6a 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -124,9 +124,14 @@ using a dynamically allocated srcu_struct (hence "srcud-" rather than debugging. The final "T" entry contains the totals of the counters. -USAGE +USAGE ON SPECIFIC KERNEL BUILDS -The following script may be used to torture RCU: +It is sometimes desirable to torture RCU on a specific kernel build, +for example, when preparing to put that kernel build into production. +In that case, the kernel should be built with CONFIG_RCU_TORTURE_TEST=m +so that the test can be started using modprobe and terminated using rmmod. + +For example, the following script may be used to torture RCU: #!/bin/sh @@ -142,8 +147,136 @@ checked for such errors. The "rmmod" command forces a "SUCCESS", two are self-explanatory, while the last indicates that while there were no RCU failures, CPU-hotplug problems were detected. -However, the tools/testing/selftests/rcutorture/bin/kvm.sh script -provides better automation, including automatic failure analysis. -It assumes a qemu/kvm-enabled platform, and runs guest OSes out of initrd. -See tools/testing/selftests/rcutorture/doc/initrd.txt for instructions -on setting up such an initrd. + +USAGE ON MAINLINE KERNELS + +When using rcutorture to test changes to RCU itself, it is often +necessary to build a number of kernels in order to test that change +across a broad range of combinations of the relevant Kconfig options +and of the relevant kernel boot parameters. In this situation, use +of modprobe and rmmod can be quite time-consuming and error-prone. + +Therefore, the tools/testing/selftests/rcutorture/bin/kvm.sh +script is available for mainline testing for x86, arm64, and +powerpc. By default, it will run the series of tests specified by +tools/testing/selftests/rcutorture/configs/rcu/CFLIST, with each test +running for 30 minutes within a guest OS using a minimal userspace +supplied by an automatically generated initrd. After the tests are +complete, the resulting build products and console output are analyzed +for errors and the results of the runs are summarized. + +On larger systems, rcutorture testing can be accelerated by passing the +--cpus argument to kvm.sh. For example, on a 64-CPU system, "--cpus 43" +would use up to 43 CPUs to run tests concurrently, which as of v5.4 would +complete all the scenarios in two batches, reducing the time to complete +from about eight hours to about one hour (not counting the time to build +the sixteen kernels). The "--dryrun sched" argument will not run tests, +but rather tell you how the tests would be scheduled into batches. This +can be useful when working out how many CPUs to specify in the --cpus +argument. + +Not all changes require that all scenarios be run. For example, a change +to Tree SRCU might run only the SRCU-N and SRCU-P scenarios using the +--configs argument to kvm.sh as follows: "--configs 'SRCU-N SRCU-P'". +Large systems can run multiple copies of of the full set of scenarios, +for example, a system with 448 hardware threads can run five instances +of the full set concurrently. To make this happen: + + kvm.sh --cpus 448 --configs '5*CFLIST' + +Alternatively, such a system can run 56 concurrent instances of a single +eight-CPU scenario: + + kvm.sh --cpus 448 --configs '56*TREE04' + +Or 28 concurrent instances of each of two eight-CPU scenarios: + + kvm.sh --cpus 448 --configs '28*TREE03 28*TREE04' + +Of course, each concurrent instance will use memory, which can be +limited using the --memory argument, which defaults to 512M. Small +values for memory may require disabling the callback-flooding tests +using the --bootargs parameter discussed below. + +Sometimes additional debugging is useful, and in such cases the --kconfig +parameter to kvm.sh may be used, for example, "--kconfig 'CONFIG_KASAN=y'". + +Kernel boot arguments can also be supplied, for example, to control +rcutorture's module parameters. For example, to test a change to RCU's +CPU stall-warning code, use "--bootargs 'rcutorture.stall_cpu=30'". +This will of course result in the scripting reporting a failure, namely +the resuling RCU CPU stall warning. As noted above, reducing memory may +require disabling rcutorture's callback-flooding tests: + + kvm.sh --cpus 448 --configs '56*TREE04' --memory 128M \ + --bootargs 'rcutorture.fwd_progress=0' + +Sometimes all that is needed is a full set of kernel builds. This is +what the --buildonly argument does. + +Finally, the --trust-make argument allows each kernel build to reuse what +it can from the previous kernel build. + +There are additional more arcane arguments that are documented in the +source code of the kvm.sh script. + +If a run contains failures, the number of buildtime and runtime failures +is listed at the end of the kvm.sh output, which you really should redirect +to a file. The build products and console output of each run is kept in +tools/testing/selftests/rcutorture/res in timestamped directories. A +given directory can be supplied to kvm-find-errors.sh in order to have +it cycle you through summaries of errors and full error logs. For example: + + tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh \ + tools/testing/selftests/rcutorture/res/2020.01.20-15.54.23 + +However, it is often more convenient to access the files directly. +Files pertaining to all scenarios in a run reside in the top-level +directory (2020.01.20-15.54.23 in the example above), while per-scenario +files reside in a subdirectory named after the scenario (for example, +"TREE04"). If a given scenario ran more than once (as in "--configs +'56*TREE04'" above), the directories corresponding to the second and +subsequent runs of that scenario include a sequence number, for example, +"TREE04.2", "TREE04.3", and so on. + +The most frequently used file in the top-level directory is testid.txt. +If the test ran in a git repository, then this file contains the commit +that was tested and any uncommitted changes in diff format. + +The most frequently used files in each per-scenario-run directory are: + +.config: This file contains the Kconfig options. + +Make.out: This contains build output for a specific scenario. + +console.log: This contains the console output for a specific scenario. + This file may be examined once the kernel has booted, but + it might not exist if the build failed. + +vmlinux: This contains the kernel, which can be useful with tools like + objdump and gdb. + +A number of additional files are available, but are less frequently used. +Many are intended for debugging of rcutorture itself or of its scripting. + +As of v5.4, a successful run with the default set of scenarios produces +the following summary at the end of the run on a 12-CPU system: + +SRCU-N ------- 804233 GPs (148.932/s) [srcu: g10008272 f0x0 ] +SRCU-P ------- 202320 GPs (37.4667/s) [srcud: g1809476 f0x0 ] +SRCU-t ------- 1122086 GPs (207.794/s) [srcu: g0 f0x0 ] +SRCU-u ------- 1111285 GPs (205.794/s) [srcud: g1 f0x0 ] +TASKS01 ------- 19666 GPs (3.64185/s) [tasks: g0 f0x0 ] +TASKS02 ------- 20541 GPs (3.80389/s) [tasks: g0 f0x0 ] +TASKS03 ------- 19416 GPs (3.59556/s) [tasks: g0 f0x0 ] +TINY01 ------- 836134 GPs (154.84/s) [rcu: g0 f0x0 ] n_max_cbs: 34198 +TINY02 ------- 850371 GPs (157.476/s) [rcu: g0 f0x0 ] n_max_cbs: 2631 +TREE01 ------- 162625 GPs (30.1157/s) [rcu: g1124169 f0x0 ] +TREE02 ------- 333003 GPs (61.6672/s) [rcu: g2647753 f0x0 ] n_max_cbs: 35844 +TREE03 ------- 306623 GPs (56.782/s) [rcu: g2975325 f0x0 ] n_max_cbs: 1496497 +CPU count limited from 16 to 12 +TREE04 ------- 246149 GPs (45.5831/s) [rcu: g1695737 f0x0 ] n_max_cbs: 434961 +TREE05 ------- 314603 GPs (58.2598/s) [rcu: g2257741 f0x2 ] n_max_cbs: 193997 +TREE07 ------- 167347 GPs (30.9902/s) [rcu: g1079021 f0x0 ] n_max_cbs: 478732 +CPU count limited from 16 to 12 +TREE09 ------- 752238 GPs (139.303/s) [rcu: g13075057 f0x0 ] n_max_cbs: 99011 |